Monoporella projecta, Arakawa, 2020

Arakawa, Shinji, 2020, Monoporella projecta (Cheilostomata: Bryozoa), a New Uniserial Species from the Continental Shelf and Slope of Japan, Species Diversity 25, pp. 219-225 : 221-222

Monoporella projecta sp. nov.

( Figs 1–4 )

Monoporella sp. : Arakawa 1999: 57, pl. 2, fig. D.

Materials examined. Holotype: NMNS PA 16855 (on a bivalve, with separated zooids from the same colony), Station 1734, Hakurei-Maru cruise GH-80-2 . Paratypes: NMNS PA 16857 (on a fragment of molluscan shell), and 18451A (on a stone, not coated with metal), Station 1734, Hakurei- Maru cruise GH-80-2. Other materials: NMNS PA 16856 (on a fragment of coral, not coated with metal), Station 1715, Hakurei-Maru cruise GH80-2; NMNS PA 18451B (opercula from 18451A), Station 1734, Hakurei-Maru cruise GH-80-2; NMNS PA 18452, SGBC-0379 and -0380 (all on fragments of molluscs), Station 1734, Hakurei-Maru cruise GH-80-2.

Diagnosis. Colony encrusting, uniserial. Frontal cryptocyst inflated, higher than low mural rim, showing tessellate surface, with scattered pores and a pair of small opesiules. Orificial rim highly projecting. Oral spines absent.

Etymology. The specific name comes from the Latin pro- jectus, referring to the highly projecting orificial rim.

Measurements (in mm). NMNS PA 16855, 16857 and 18452; SGBC-0379 and -0380. Autozooids (24, 4): ZL, 0.99– 1.52 (1.300±0.166); ZW, 0.63–0.91 (0.710±0.061); OrL, 0.11–0.16 (0.141±0.013); OrW, 0.15–0.21 (0.175±0.015).

Description. Colony encrusting, uniserial; zooids generally budding one or two zooids, rarely three ( Figs 1 , 2A, B ). Zooids elliptical, much inflated. Lateral wall very low, with pair of large communication pores laterally and one distally. Frontal wall cryptocystal, inflated above low mural rim, finely granulated; granules aligned to form reticulum of narrow ridges ( Fig. 3A, B ), and perforated with scattered pores; median carina sometimes observed ( Fig. 2C, D ); interior of frontal wall nearly smooth, with tube structure connecting small opesiules ( Fig. 3C ). Orifice semicircular, with straight or slightly concave proximal border, bearing small shelf in each proximo-lateral corner, sometimes with a pair of round condyles; vestibular arch well-developed, crenulated, often boomerang-shaped inside ( Fig. 4A, B ). Orificial rim highly projecting ( Fig. 2D ), about 0.3 mm tall; its surface finely granulated, not tessellate ( Fig. 3D ). Oral spines absent. Operculum black; outer surface smooth, not pitted; inner surface with thin central area and proximolateral crests for attachment of occlusor muscles ( Fig. 4C, D ). Ovicell not found. Avicularia absent. Ancestrulae resembling subsequent autozooids, not so small (zooid “a” in Fig. 2A , zooid “0” in Fig. 2B ).

Distribution. Presently known only from the eastern continental shelf and slope of the Boso Peninsula, Japan. The bathymetrical range is from 144 m to 350 m in depth.

Remarks. This species is characterized by the uniserial colony form, the highly inflated cryptocyst and the projecting orificial rim.

It has a smooth operculum in common with all of six Monoporella species from the Aleutian Islands ( Dick 2008), and four of which ( Monoporella flexibila Dick, 2008 , M. elongata Dick, 2008 , M. ellefsoni Dick, 2008 , M. aleutica Dick, 2008 ) also lack oral spines. Among these, M. flexibila is most similar to M. projecta in having a low mural rim and in the obscurity of the marginal boundary of cryptocyst, especially in the initial encrusting portion of the colony.

The frontal wall of Monoporella projecta resembles the tessellate cryptocyst in M. flexibila and M. elongata , but the concavities in the cryptocyst of this species are shallower and broader than in the latter two species, and the bottom of each concavity is also generally granulated ( Figs 2D , 3A ). In addition, the surface of the orificial rim is not pitted in M. projecta .

Figures

Fig. 1. Colonies of Monoporella projecta sp. nov. A, holotype, NMNS PA 16855; B, paratype, NMNS PA 18451A. Scale bars: 1mm.

Fig. 2. Autozooids. A, holotype, NMNS PA 16855, ancestrulae “a” and subsequent zooids; B, paratype, NMNS PA 16857, ancestrulae “0” and subsequent zooids; C, zooid “L4” in A, separated from the substrate by cleaning; D, zooid “3” in B, moved from the original position. Scale bars: 1mm in A, B, and 200µm in C, D.

Fig. 3. Autozooids of holotype. A, close-up of frontal cryptocyst and orificial rim (lower-left), zooid “a” in Fig. 2A; B, close-up of frontal cryptocyst, zooid “R3” in Fig. 2A; C, inner side of frontal wall with a tube structure connecting an opesiule (arrow), basal wall broken; D, zooid of the lower-right row in Fig.1A, moved from the original position. Scale bars: 20µm in A, B and 200µm in C, D.

Fig. 4. Orifice and operculum. A, orifice of zooid L4 in Fig. 2A; B, orifice of one zooid of the lower-right row in Fig. 1A; C, outer surface of operculum, NMNS PA 18451B; D, inner surface of operculum, NMNS PA 18451B. Scale bars: 50µm.